Diagbox and obd reader are reading different values on same senor???

[jmmj]

Hi folks,

I have a recent full chip 'diagbox' clone and a cheap obd2 bluetooth reader.

I have a pinging issue and wanted to look at the MAP sensor. Map readings should follow the TPS (throttle body position). On the obd reader it seems to be functioning fine as tested in two different apps. In diagbox, i have a correct readings at idle, but if i step on the accelerator the mbar value goes DOWN when pressure should be increasing?!?!

What does one do in this case??

Cheers,

Mike

[Arfur Dent]

Hi folks,

I have a recent full chip 'diagbox' clone and a cheap obd2 bluetooth reader.

I have a pinging issue and wanted to look at the MAP sensor. Map readings should follow the TPS (throttle body position). On the obd reader it seems to be functioning fine as tested in two different apps. In diagbox, i have a correct readings at idle, but if i step on the accelerator the mbar value goes DOWN when pressure should be increasing?!?!

What does one do in this case??

Cheers,

Mike

Hi

I would go with what Diagbox says because that is the dealer tool. You may need to update diagbox version if it doesn't work fully with your model.


As for cheap OBD readers, they are probably based on the same chip so carry the same error. I would take Diagbox/Lexia over OBD clones every time.

[jmmj]

Cheers Arfur!

Its strange, that was in the custom selected parameters pane. While in the standard parameters section the result was different. Well, i decided to hold the pedal down for a few seconds instead of just blips. So the pressure reading did actually go up. I think its a refresh rate thing, diagbox just seems really, really slow. Maybe its the computer, even though its dedicated to diagbox it is old?!!

[Arfur Dent]

I don't know which laptop you are running on. But lexia can run on some very old hardware. Diagbox needs a bit newer for Windows 7.

A faster laptop may be better?

Maybe it won't make any difference?

[Ozvtr]

Simple OBDII readers don't have an operating system and I/O issues to deal with. And laptops are ssssooooo slow.

You are better off logging the data. Then studying (comparing) the traces. Like, MAP Vs TPS. It's a lot slower but you can get more information out of it.

Yes, a cheap 15 pound OBDII is very good for spotting basic engine problems. It's quick and you don't need to drag a laptop around. But when it comes to scanning and trouble shooting the other ECUs, LEXIA represents better value for money. While I have not used it, apparently there is an EOBD scanner in one of the versions of Diagbox. Arfur might know a bit more about that.

I have a pinging issue

Have you logged engine load vs timing advance? As the load gets greater the timing should retard. The engine ECU will advance the timing until the knock sensor complains. If the knock sensor is un-serviceable, the ecu will keep advancing the timing. Not sure if there is an option to log knock sensor 'hits'. Knock sensors are difficult to test.
Could be crap fuel? Even at max retard bad fuel can ping.